- Port-based VLANs are commonly used today, where a port is associated with a VLAN. - Data VLANs carry only user traffic, separating it from voice and management traffic. The default VLAN on Cisco switches is VLAN 1. - A native VLAN is assigned to trunk ports to handle untagged traffic using VLAN 99 as an example. A management VLAN like VLAN 99 provides switch management access. Voice VLANs use a separate VLAN like VLAN 150 to ensure quality of voice traffic.

1. Types of VLANs/VLAN Types
Nowadays, there is essentially one way of implementing VLANs - port-based VLANs.
A port-based VLAN is associated with a port called an access VLAN.
However in the network there are a number of terms for VLANs. Some terms define
the type of network traffic they carry and others define a specific function a VLAN
performs. The following describes common VLAN terminology:
Data VLAN
A data VLAN is a VLAN that is configured to carry only user-generated traffic. A VLAN
could carry voice-based traffic or traffic used to manage the switch, but this traffic
would not be part of a data VLAN. It is common practice to separate voice
and management traffic from data traffic. The importance of separating user data
from switch management control data and voice traffic is highlighted by the use of a
special term used to identify VLANs that only carry user data - a "data VLAN". A data
VLAN is sometimes referred to as a user VLAN.
Default VLAN
All switch ports become a member of the default VLAN after the initial boot up of the
switch. Having all the switch ports participate in the default VLAN makes them all
part of the same broadcast domain. This allows any device connected to any switch
port to communicate with other devices on other switch ports. The default VLAN
for Cisco switches is VLAN 1.
VLAN 1 has all the features of any VLAN, except that you cannot rename it and you
cannot delete it. Layer 2 control traffic, such as CDP and spanning tree protocol
traffic, will always be associated with VLAN 1 - this cannot be changed. In the figure,
VLAN 1 traffic is forwarded over the VLAN trunks connecting the S1, S2, and S3
switches. It is a security best practice to change the default VLAN to a VLAN other
than VLAN 1; this entails configuring all the ports on the switch to be associated with
a default VLAN other than VLAN 1. VLAN trunks support the transmission of traffic
from more than one VLAN. Although VLAN trunks are mentioned throughout this
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2. section, they are explained in the next section on VLAN trunking.
Note:Some network administrators use the term "default VLAN" to mean a VLAN
other than VLAN 1 defined by the network administrator as the VLAN that all ports
are assigned to when they are not in use. In this case, the only role that VLAN 1 plays
is that of handling Layer 2 control traffic for the network.
Native VLAN
A native VLAN is assigned to an 802.1Q trunk port. An 802.1Q trunk port supports
traffic coming from many VLANs (tagged traffic) as well as traffic that does not come
from a VLAN (untagged traffic). The 802.1Q trunk port places untagged traffic on the
native VLAN. In the figure, the native VLAN is VLAN 99. Untagged traffic is generated
by a computer attached to a switch port that is configured with the native VLAN.
Native VLANs are set out in the IEEE 802.1Q specification to maintain backward
compatibility with untagged traffic common to legacy LAN scenarios. For our
purposes, a native VLAN serves as a common identifier on opposing ends of a trunk
link. It is a best practice to use a VLAN other than VLAN 1 as the native VLAN.
Management VLAN
A management VLAN is any VLAN you configure to
accessthe management capabilities of a switch.VLAN 1 would serve
asthe management VLAN if you did not proactively define a unique VLAN to serve as
the management VLAN. You assign the management VLAN an IP address and subnet
mask. A switch can be managed via HTTP, Telnet, SSH, or SNMP. Since
theout-of-the-box configuration of a Cisco switch has VLAN 1 as the default VLAN,
you see that VLAN 1 would be a bad choice as the management VLAN; you wouldn't
want an arbitrary user connecting to a switch to default to the management VLAN.
Recall that you configured the management VLAN as VLAN 99 in the Basic Switch
Concepts and Configuration chapter.
Voice VLANs
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3. It is easy to appreciate why aseparate VLAN is needed to support Voice over IP (VoIP).
Imagine you are receiving an emergency call and suddenly the quality of the
transmission degrades so much you cannot understand what the caller is
saying. VoIPtraffic requires:
Assured bandwidth to ensure voice quality
Transmission priority over other types of network traffic
Ability to be routed around congested areas on the network
Delay of less than 150 milliseconds (ms) across the network
To meet these requirements, the entire network has to be designed to support VoIP.
The details of how to configure a network to support VoIP are beyond the scope of
the course, but it is useful to summarize how a voice VLAN works between a switch,
a Cisco IP phone, and a computer.
In the figure, VLAN 150 is designed to carry voice traffic. The student computer PC5 is
attached to the Cisco IP phone, and the phone is attached to switch S3. PC5 is in
VLAN 20, which is used for student data. The F0/18 port on S3 is configured to be in
voice mode so that it will tell the phone to tag voice frames with VLAN 150. Data
frames coming through theCisco IP phone from PC5 are left untagged. Data destined
for PC5 coming from port F0/18 is tagged with VLAN 20 on the way to the phone,
which strips the VLAN tag before the data is forwarded to PC5. Tagging refers to the
addition of bytes to a field in the data frame which is used by the switch to identify
which VLAN the data frame should be sent to.
A Cisco Phone is a Switch
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4. The Cisco IP Phone contains an integrated three-port 10/100 switch as shown in the
Figure. The ports provide dedicated connections to these devices:
Port 1 connects to the switch or other voice-over-IP (VoIP) device.
Port 2 is an internal 10/100 interface that carries the IP phone traffic.
Port 3 (access port) connects to a PC or other device.
The figure shows one way to connect an IP Phone.
The voice VLAN feature enables switch ports to carry IP voice traffic from an IP phone.
When the switch is connected to an IP Phone, the switch sends messages that
instruct the attached IP phone to send voice traffic tagged with the voice VLAN ID
150. The traffic from the PC attached to the IP Phone passes through the IP phone
untagged. When the switch port has been configured with a voice VLAN, the link
between the switch and the IP phone acts as a trunk to carry both the tagged voice
traffic and untagged data traffic.
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5. Sample Configuration
The figure shows sample output. A discussion of the Cisco IOS commands are beyond
the scope of this course, but you can see that the highlighted areas in the sample
output show the F0/18 interface configured with a VLAN configured for data (VLAN
20) and a VLAN configured for voice (VLAN 150).
More aboutVLAN Types
How a Switch distinguishes between VLANs? This is done by associating the work
stations to a specific VLAN using specified format. This is known as VLAN
membership. Four prominent VLAN membership methods are by port, MAC address,
protocol type, and subnet address. Each of these is discussed below:
1. VLAN membership by Port:
Here, you define which ports of a Switch belong to which VLAN. Any work station
connected to a particular port will automatically be assigned that VLAN. For example,
in a Switch with eight ports, ports 1-4 may be configured with VLAN 1, and ports 5-8
may be configured with VLAN2.
One of the disadvantages of this method is that it requires Switch port
reconfiguration whenever a user (of course, with associated workstation) moves
from one place to another. VLANs by port association operate at Layer 1 of the OSI
model.
2. VLAN membership by MAC Address:
Here, membership in a VLAN is based on the MAC address of the user workstation. A
Switch that participates in VLAN uses the MAC addresses to assign a VLAN to each
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6. workstation. When a workstation moves to another place, the corresponding switch
automatically discovers the VLAN association based on the MAC address of the
workstation. Since the MAC address is normally inseparable from that of the
workstation, this method of VLAN membership is more amenable to workstation
moves.
This type of VLAN works at Layer 2 of the OSI model.
3. Membership by Protocol Type:
Layer 2 header contains the protocol type field. You can use this information to
decide on the VLAN association. For example, all IP traffic may be associated with
VLAN 1 and all IPX traffic may be associated with VLAN 2.
4. Membership by IP Subnet Address
In this type of VLAN association, membership is based on the Layer 3 header. The
Switch reads the Layer 3 IP address and associates a VLAN membership. Note that
even though the Switch accesses Layer 3 information, it still works at Layer 2 of OSI
model only. A VLAN Switch doesn't do any routing based on IP address.
Examples:
IP Subnet VLAN
192.23.160.0 1
192.23.161.0 2
112.18.0.0 3
IP Subnet addresses assignment to different VLAN's.
IP address based VLANs allow user moves. However, it is likely to take more time to
forward a packet by a Switch because it has to read Layer 3 information. Hence the
latency rates may be relatively more using this type of VLAN membership.
More Related Networking Tips:
‘What Happens in the VLAN Stays in the VLAN?’
How Private VLANs Work?
How to Configure Private VLANs on Cisco 3560 Switches?
VLAN Trunking Protocol (VTP) & VTP Modes
Types of Networks
VLAN Switch Port Modes
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